Automatic injection device

ABSTRACT

A device is provided for automatic injection of a product comprising a container, a needle and a piston. The device includes a housing receiving the container, the container being movable with respect to the housing between an initial position and an insertion position, distally spaced relative to the initial position; a safety shield coupled to the housing and movable with respect thereto between a rest position, an activation position, proximally spaced relative to the rest position, and a safety position; biasing feature for causing the movement of the safety shield to the safety position; triggering feature for causing the container to move from its initial position to its insertion position, the triggering feature being releasable by movement of the safety shield to the activation position; and, isolating feature for isolating the safety shield from the biasing feature when the safety shield is moved to its activation position.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.13/120,676, filed May 19, 2011, now U.S. Pat. No. 8,696,628 B2, which isa National Stage Application under §371 of PCT Application No.PCT/IB2008/003290, filed Sep. 29, 2008, the entireties of which areincorporated by reference herein.

BACKGROUND OF THE INVENTION

The present invention relates to a device for automatic injection of aproduct, especially for self-injection, so that the use of the device isas atraumatic as possible for the patient.

In this application, the distal end of a component or of a device is tobe understood as meaning the end furthest from the user's hand and theproximal end is to be understood as meaning the end closest to theuser's hand. Likewise, in this application, the “distal direction” is tobe understood as meaning the direction of injection, and the “proximaldirection” is to be understood as meaning the opposite direction to thedirection of injection.

Some illnesses necessitate regular injections of drugs or products, forinstance on a daily basis. In order to simplify the treatment, someself-injectors have been provided in order to allow the patient toperform the injection on its own.

Of course, since the patient is usually neither a nurse nor an educatedperson in medical devices, such self-injectors must prove to be verysimple to use and also very safe. In particular, the insertion of theneedle must be performed at the right depth, the correct dose of productmust be injected, that is to say a complete injection must be performed,and the injector must be deactivated after use before it is disposed of.Preferably, the needle should not be exposed, before and after use, inorder to prevent any accidental needlestick injury. Usually, suchself-injectors are provided with a safety shield in order to protect theneedle before use and after use.

Another important requirement of these self-injection devices is thatthey must not be able to be activated inadvertently, before the patientis ready to perform the injection, and in particular before the deviceis correctly applied at the right injection site.

Such self-injectors with automatic insertion and injection steps, and asafety shield in order to protect the needle after use have beendescribed in document WO2007/132353. This document describes a devicefor automatic injection in which the injection cannot be triggeredbefore the device is correctly in place. In particular, the user needsto push distally on an external housing of the device, once the deviceis applied on the injection site, in order to be allowed to trigger theinjection. Nevertheless, in order to complete this step, the user has toovercome the force of biasing means intended to cause the automaticextension of the safety shield after use. The force of these biasingmeans is usually high and the consequence is that the user may be hurtor may feel a bad sensation on the skin when accomplishing the step ofpushing distally on the external housing of the device for placing thedevice correctly and being allowed to trigger the injection. This badfeeling may refrain the user/patient from carrying on the administrationof the product.

There is therefore a need for an automatic injection device that wouldbe safe but at the same time would allow the user/patient to put thedevice correctly in place without feeling badly or feeling too high apressure on the skin at the injection site.

The present invention meets this need by proposing a device forautomatic injection of a product into an injection site, said devicecomprising a safety system for preventing the triggering of theinjection when the device is not correctly placed on the site ofinjection, a safety shield capable of being deployed automatically atthe end of injection under the effect of biasing means, and means forcancelling the force of said biasing means felt by the patient when saiduser/patient completes the step of deactivating the safety system.

The present invention relates to a device for automatic injection of aproduct into an injection site, the product being carried by a containerhaving an open proximal end and a substantially closed distal end andcarrying a needle to provide an outlet port for the product from thecontainer, and a piston provided in the container and movable withrespect to the container, the movement of the piston causing the productto be expelled from the container through the needle,

a housing receiving at least partially said container, said containerbeing movable with respect to said housing between an initial position,in which a tip of the needle does not extend beyond a distal end of saidhousing, and an insertion position, distally spaced relative to saidinitial position, and in which the tip of the needle extends beyond saiddistal end of said housing,

a safety shield coupled to said housing and movable with respect theretobetween a rest position, an activation position, proximally spacedrelative to said rest position, and a safety position, distally spacedwith respect to said rest position,

biasing means for causing the movement of said safety shield to saidsafety position,

triggering means for causing the container to move from its initialposition to its insertion position, said triggering means beingreleasable by movement of said safety shield to said activationposition,

characterized in that said device further comprises:

isolating means for isolating said safety shield from said biasing meanswhen said safety shield is moved to its activation position.

The device of the invention provides for a very safe device, whichcannot be triggered as long as it is not correctly located at theinjection site and which does not hurt the user during the step ofdeactivating the safety system, said safety system being formed by thefact that the triggering means cannot be activated as long as the safetyshield has not moved from its rest position to its activation position.Moreover, in the device of the invention, the needle is automaticallyprotected after use thanks to biasing means deploying the safety shield.In particular, because of the presence of specific isolating means inthe device of the invention, the patient does not feel the force of thebiasing means during the step of moving the safety shield from its restposition to its activation position.

In an embodiment of the invention, said isolating means comprise a firstring, receiving said container, said first ring being coupled to saidbiasing means in the proximal direction and coupled to said housing inthe distal direction, and being independent from said safety shield, atleast when said safety shield is moved to its activation position.

In the present application, by the expression “A is coupled to B in theX direction”, one means that A is linked to B when A is moved in the Xdirection: in other words, when A is coupled to B in the X direction,then if A is caused to move in the X direction, then B is also caused tomove in the X direction.

In the present application, by the expression “A is free or independentfrom B”, one means that A is not coupled to B.

In an embodiment of the invention, said first ring comprises at least aflexible tooth provided with a distal abutment surface and said housingcomprises at least a radial stop, said first ring being coupled to saidhousing in the distal direction by means of said distal abutment surfaceresting on said radial stop, when said safety shield is moved to itsactivation position.

In an embodiment of the invention, said device further comprises asecond ring, said second ring being fixed to the proximal region of saidcontainer and being proximally spaced with respect to said first ringwhen said safety shield is moved to its activation position, saidbiasing means comprising a helical spring, a proximal end of saidhelical spring bearing on a part of said second ring and a distal end ofsaid helical spring bearing on a part of said first ring.

In an embodiment of the invention, said flexible tooth comprises aproximal sloping surface and said second ring comprises a distal slopingsurface, said distal sloping surface being capable to come in abutmentagainst said proximal sloping surface so as to deflect said flexibletooth and disengage said flexible tooth from said radial stop, therebyfreeing said first ring from said housing when said container is in itsinsertion position.

In an embodiment of the invention, said safety shield comprises at leastone radial rim, said radial rim being located in regards to the distalface of said first ring, said distal face of said first ring coming inabutment against said radial rim when said container is in its insertionposition, thereby coupling said first ring to said safety shield in thedistal direction under the biasing force of the biasing means.

The device of the invention will now be further described in referenceto the following description and attached drawings in which:

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a longitudinal cross section view of an embodiment of thedevice of the invention before use,

FIG. 2 is a longitudinal cross section view of the device of FIG. 1,after deactivation of the safety system,

FIG. 3 is a longitudinal cross section view of the device of FIG. 1 atthe time of activation of the triggering means,

FIG. 4 is a longitudinal cross section view of the device of FIG. 1 oncethe container is in its insertion position,

FIG. 5 is a longitudinal cross section view of the device of FIG. 1 atthe end of injection.

Referring now to the drawings, the present invention will now bedescribed in detail. FIG. 1 shows a longitudinal cross section view of adevice for automatic injection according to an embodiment of the presentinvention and generally designated by reference number 1. The device 1of the invention comprises a container 2 carrying a product 3 to beinjected into an injection site 4 (see FIGS. 2-5). The container 2 hasan open proximal end 2 a provided with a flange 5 and a substantiallyclosed distal end 2 b bearing an injection needle 6. Lateral walls 2 cof the container 2 extend between the proximal and distal ends (2 a, 2b) and define a reservoir 2 d sized and shaped to contain apredetermined amount of a product 3 for injection. The injection needle6 may be fixed to the distal end 2 b of the container 2, or removabletherefrom, as a matter of design choice. The injection needle 6 is influid communication with the reservoir 2 d and provides an outlet portfor the product 3 from the container 2. A piston 7 is provided in thecontainer and movable with respect to the container 2: as will appearfrom FIG. 5, the distal movement of the piston 7 is intended to causethe product 3 to be expelled from the container 2 through the needle 6.A needle shield (not represented) may be provided at the distal end 2 bof the container 2 to cover and protect the needle 6 before use of thedevice 1.

The device 1 of FIGS. 1-5 further comprises a safety shield 8 receivingat least partially said container 2. On the example shown, the safetyshield 8 has a general tubular shape with an open proximal end 8 a andan open distal end 8 b. The proximal end 8 a of the safety shield 8 isprovided with at least one radial rim 9 prolonged by a longitudinal leg10 extending in the proximal direction. The longitudinal leg 10 isprovided with a window 11 separating a proximal portion 10 a of said leg10 from a distal portion 10 b of said leg 10.

The device 1 of FIGS. 1-5 further comprises a housing 12 receiving atleast partially said container 2 and said safety shield 8. On theexample shown, the housing 12 has a general tubular shape with an openproximal end 12 a and an open distal 12 b.

The housing 12 is provided on its internal wall with at least a flexibleleg 13 extending in the proximal direction. The flexible leg 13 iscapable of being deflected from a free position in which it extendsradially inwardly (see FIG. 1), to a stressed position in which itextends longitudinally parallel to the walls of the housing 12 (see FIG.2).

The housing 12 further comprises a radial stop 14 located on theinternal wall of said housing 12.

In its proximal region, the housing 12 is further provided with an innercylinder 15 linked to the housing 12 via a radial wall 16. The innercylinder 15 has an open proximal end 15 a and an open distal end 15 b.The cylinder 15 is provided at its proximal end 15 a with at least aninner radial rim 17 and with at least a flexible tooth 18 provided witha proximal abutment surface 18 a.

The inner cylinder 15 is provided on its outer wall with a flexibletongue 19 extending in the proximal direction. The flexible tongue 19 iscapable of being deflected from a free position, in which it extendsradially outwardly with respect to the inner cylinder 15 (see FIG. 1)and a stressed position, in which it extends longitudinally, parallel tothe walls of the inner cylinder 15 (see FIG. 2).

At its proximal end 12 a, the housing 12 is provided on its inner wallwith a radial abutment surface 20.

As will appear from the following description of FIGS. 1-5, thecontainer 2 is movable with respect to said housing 12 between aninitial position, in which a tip 6 a of the needle 6 does not extendbeyond a distal end 12 b of said housing (see FIGS. 1-3) and aninsertion position, distally spaced relative to said initial position,in which the tip 6 a of the needle 6 extends beyond said distal end 8 bof said safety shield 8 (see FIG. 4).

The device 1 of FIGS. 1-5 is further provided with a piston rod 21intended to push distally the piston 7 in order to expel the product 3out of the container 2 and realise the injection. On the example shown,the piston rod 21 is provided at its proximal end with a radial stop 22and at its distal end with a radial flange 23.

The device 1 of FIGS. 1-5 further comprises a first ring 24 and a secondring 25, both rings (24, 25) receiving the container 2. The second ring25 is proximally spaced with respect to said first ring 24.

The first ring 24 has a proximal face 24 a and a distal face 24 b. Thefirst ring 24 further comprises a flexible tooth 26, extending in theproximal direction from the proximal face of said first ring 24, saidflexible tooth 26 being provided with a distal abutment surface 26 a andwith a proximal sloping surface 26 b. As shown on FIGS. 1 and 2, beforethe insertion step, the distal abutment surface 26 a of the first ring24 rests on the radial stop 14 of the housing 12.

The second ring 25 is fixed to the flange 5 of the container 2 byclassical fixation means (not shown) such as clips, glue, etc. . . . Thesecond ring 25 has a proximal face 25 a and a distal face 25 b. Thesecond ring 25 is further provided with a distal sloping surface 27 andwith a distal skirt 28.

The device 1 of FIGS. 1-5 further comprises a push button 29 partiallyreceived within the distal region of the housing 12. The push button 29has the general shape of a tube closed at its proximal end by a pushingwall 30 and open at its distal end. The pushing wall comprises on itsinner face a peg 31 extending distally. The pushing button 29 isprovided at its distal end with an outer projection 32.

A first helical spring 33 is provided around the container 2 and betweenthe first ring 24 and the second ring 25. As shown on FIG. 1, theproximal end of the first helical spring 33 bears on the distal skirt 28of the second ring 25 and the distal end of the first helical spring 33bears on the proximal face 24 a of the first ring 24.

A second helical spring 34 is provided around the piston rod 21. Asshown on FIG. 1, the proximal end of the second helical spring 34 bearson the inner radial rim 17 of the inner cylinder 15 and the distal endof the second helical spring 34 bears on the proximal face of the flange23 of the piston rod 21.

As will appear from the following description, the safety shield 8 iscoupled to said housing 12 and movable with respect thereto between arest position, an activation position, proximally spaced relative tosaid rest position, and a safety position, distally spaced with respectto said rest position. As will also appear from the description, thepush button 29 is intended to be used as triggering means for activatingthe injection, said triggering means being releasable by movement ofsaid safety shield 8 to its activation position.

The functioning of the device 1 will now be explained in reference toFIGS. 1-5. Before providing a detailed description of the operation of adevice 1 constructed in accordance with the present invention, thefollowing general description of its operation is provided. Theinventive device 1 is provided to a user ready-to-use. The container 2is filled with a predetermined dose of an injectable product 3. At thetime of use, the user places the device 1 against his/her skin at aninjection site 4 and applies a distal force on the housing 12. As thehousing 12 is pressed distally, the safety shield 8 is caused to move inthe proximal direction and into the housing 12. Due to a safety systemof the inventive device 1, a user cannot activate the device 1 (i.e.,cause the container 2 to move from its initial position to its insertionposition) until the safety shield 8 is caused to move a predetermineddistance in the proximal direction with respect to the housing 12.Indeed, the container 2 is in a passive state, ie is not allowed to movefrom its initial position to its insertion position, as long as thesafety shield 8 has not moved on said predetermined distance. With thedevice 1 pressed against his/her skin (and the safety shield 8 moved onsaid distance in the proximal direction), the container 2 adopts anactive state, and the user can activate the device 1 and press the pushbutton 29. That will cause the container 2 to move from its initialposition to its insertion position, which also causes the needle 6 topierce the user's skin. The injection may then be realised. Once theinjection is complete, the user removes the device 1 from the injectionsite and the safety shield 8 is caused to automatically extend from thehousing 12 to cover the now-contaminated tip 6 a of the needle 6.Advantageously, even if the user removes the device 1 from the injectionsite 4 before the injection is complete, the safety shield 8 willautomatically extend over the tip of the needle. Once the device 1 isremoved from the injection site 4 and the shield 8 is extended over thetip of the needle 6, the shield 8 locks in place and cannot thereafterbe moved from its locked position in the proximal direction to exposethe tip 6 a of the needle 6. The used device 1 is thus rendered safe forhandling and disposal.

On FIG. 1 is shown the device 1 before use, as provided to the user. Inthis position, the flexible leg 13 of the housing is in its freeposition and extends radially inwardly: as shown on FIG. 1, saidflexible leg 13 therefore protrudes through the window 11 of thelongitudinal leg 10 of the safety shield 8 and engages the distal face25 b of the second ring 25. The container 2 is by consequence in apassive state: it cannot move distally. Moreover, in the before useposition of FIG. 1, the flexible tongue 19 of the inner cylinder 15 isalso in its free position: that is to say that said flexible 19 extendsradially outwardly with respect to said cylinder 15. As shown on FIG. 1,in this position, said flexible tongue 19 faces the distal end of thepush button 29. Thus, if the user pushes on the push button 29, thedistal end of the push button 29 abuts on the flexible tongue 19 and thedistal movement of the push button 29 is stopped before the peg 31reaches the flexible tooth 18 of the inner cylinder 15. The triggeringmeans, i.e. the push button 29, is therefore in a locked position andcannot be released. As shown on FIG. 1, said flexible tooth 18, by itsproximal abutment surface 18 a being engaged in the radial stop 22 ofthe piston rod 21, prohibits any freeing of the second helical spring34: the movement of the container 2 to its insertion position is notpossible. In consequence, in the position of FIG. 1, the injectioncannot be activated. The device 1 of the invention is particularly safeand cannot be activated as long as it is not correctly placed on theinjection site. The flexible tongue 19 and the flexible leg 13contribute to the ability of the device 1 to adopt a locked position andtherefore form part of the safety system of the device of the invention.

In the position shown on FIG. 1, the first helical spring 33 is in apartially compressed state and the second helical spring 34 is in acompressed state. As appears from FIG. 1, the first helical spring 33 iscompressed between the first ring 24 and the second ring 25. Moreover,the first ring 24 is in abutment on the radial stop 14 of the housing 12by means of the distal abutment face 26 a of said first ring 24 restingon said radial stop 14. As a consequence, in this before use position asshown on FIG. 1, the safety shield 8 is not coupled to the first helicalspring 33: in other words, the safety shield 8 is independent and freefrom said first helical spring 33. The first ring 24 therefore acts asan isolating means for isolating or freeing said safety shield 8 fromsaid first helical spring 33. The safety shield 8 is thus allowed tomove with respect to the housing 12 without interacting with the firsthelical spring 33.

In this position of the device 1, the tip 6 a of the needle 6 isprotected by the housing 12 whose distal end 12 b extends beyond saidtip 6 a of the needle 6. In this position of the device 1 also, thesafety shield 8 is in a rest position.

When the user wishes to proceed with the administration of the product3, he applies the device 1 on the skin of the patient at the injectionsite 4 and pushes the housing 12 distally, as shown on FIG. 2, therebycausing the safety shield 8 to move with respect to said housing 12 fromits rest position to an activation position, proximally spaced relativeto said rest position. During this step, as explained hereinabove, thefirst ring 24 is coupled to the biasing means, ie the helical spring 33,in the proximal direction and coupled to the housing 12 in the distaldirection by means of said distal abutment surface 26 a resting on saidradial stop 14, and it is independent or isolated from said safetyshield 8. As a consequence, the safety shield 8 is free or isolated fromthe first helical spring 33 and it does not interact with said firsthelical spring 33. The patient has therefore no bad feeling on the skin:the patient does not feel the force of the first helical spring 33. Thepatient feels better at ease and is not hurt during this step. Thiscontributes to a safer use of the device 1 for the patient/user.

As shown on FIG. 2, while the user/patient has pushed distally on thehousing 12, the safety shield 8 has moved proximally with respect to thehousing 12. As a consequence, the distal part 10 b of the longitudinalleg 10 has come in abutment on the flexible leg 13 of the housing 12 andhas put it under stress, forcing it to deflect so as to reach a positionparallel to the wall of the housing 12, as shown on FIG. 2. The flexibleleg 13 of the housing 12 has therefore disengaged from the distal face25 b of the second ring 25. At the same time and as a consequence of thesame movement, the proximal part 10 a of the longitudinal leg 10 of thesafety shield 8 has come in abutment on the flexible tongue 19 of theinner cylinder 15 and has deflected it, forcing it to reach a positionwhere said flexible tongue 19 is parallel to the wall of the innercylinder 15: as shown on FIG. 2, in this position, the flexible tongue19 no longer faces the distal end of the push button 29.

The push button 29 is linked to the housing 12 by means of its outerprojection 32 being engaged in the radial abutment surface 20 of thehousing 12; such an engagement allows the push button 29 to movedistally with respect to the housing if a user exerts a distal pressureon the pushing wall 30 of the push button.

As appears clearly from FIG. 2, the device 1 and/or the container 2 arenow in their active state: the flexible leg 13 is disengaged and theflexible tongue 19 is also disengaged. The safety shield 8 is now in itsactivation position. The triggering means, ie the push button 29, maynow be released and insertion of the container 2 can be triggered.

In order to trigger the insertion of the container 2, the user pushesdistally on the pushing wall 30 of the push button 29 which acts astriggering means. As shown on FIG. 3, as a consequence of the safetyshield 8 having moved to its activation position, the push button 29 isnow allowed to move distally with respect to the housing 12 and the peg31 of the push button 29 comes in abutment against the flexible tooth 18of the inner cylinder 15, said flexible tooth 18 being thereby caused todeflect radially outwardly. As a consequence, the radial stop 22 of thepiston rod 21 disengages from the proximal abutment surface 18 a of theflexible tooth 18 of the inner cylinder 15 and the second helical spring34 is freed.

The second helical spring 34 tends to come back to its expanded stateand causes the distal movement of the piston rod 21. The piston rod 21comes in abutment on the piston 7. The friction force of the piston 7against the inner walls of the container 2 being higher than the forceof the second helical spring 34, the container 2 is also caused to movedistally under the effect of the expansion of the second helical spring34.

As shown on FIG. 4, the distal movement of the container 2 causes theinsertion of the needle 6 in the injection site 4. At the same time, andas a consequence of the same movement, the distal sloping surface 27 ofthe second ring 25 has come in abutment on the proximal sloping surface26 b of the first ring 24, causing the flexible tooth 26 to deflectinwardly radially and to disengage from the radial stop 14 of thehousing 12, as shown on FIG. 4. As a consequence, said first ring 24 isfreed from said housing 12. The first ring 24 is no more coupled to thehousing 12 in the distal direction. Moreover, in this insertionposition, the distal face 24 b of the first ring 24 is in abutmentagainst the radial rim 9 of the safety shield 8: as a consequence, thefirst ring 24 is now coupled to the safety shield 8 in the proximaldirection under the biasing force of the first helical spring 33. Thefirst helical spring 33 is now in a compressed state and the container 2is thereby caused to be stopped at a predetermined insertion depth. Thesecond helical spring 34 in the example shown, acts as automaticinjection means.

The force of the second helical spring 34 is therefore allowed toovercome the friction force of the piston 7 against the inner walls ofthe container 2 and the piston rod 21 is caused to push the piston 7distally so as to realise the injection, as shown on FIG. 5.

At the end of injection, as shown on FIG. 5, the flexible tooth 26 ofthe first ring 24 is still disengaged from the radial stop 14 of thehousing 12. As a consequence, when the user withdraws the device 1 fromthe injection site, the first helical spring 33, which is now coupled tothe safety shield 8 in the distal direction, is free to expand anddeploy the safety shield 8 over the needle 6 (step not shown); thesafety shield 8 is therefore in its safety position, distally spacedfrom its rest position, and in which it covers the needle 6 therebypreventing any needle stick injury. The device of the invention istherefore particularly safe.

As can be noticed from FIG. 4, the flexible tooth 26 is disengaged fromthe radial stop 14 of the housing 12 as soon as the injection starts. Asa consequence, if the user inadvertently withdraws the device 1 of theinvention from the injection site 4 before the end of the injection, thesafety shield 8 will automatically expand over the needle 6 and willprevent any needle stick injury.

The device of the invention provides for a very safe device, whichcannot be triggered as long as it is not correctly located at theinjection site and which does not hurt the user during the step ofdeactivating the safety system. In particular, because of the presenceof specific isolating means, the user does not feel the force of thebiasing means intended to expand the safety shield at the end ofinjection.

The injection device of the invention also allows automatic injection ofa product to be performed by a patient without any risk of needlestickinjury, before, during and after use. In particular, the safety shieldof the device of the invention is in its active state right at the endof the insertion step, before the injection step actually begins. Inthis way, even if the patient decides to withdraw the device before theend of the injection, then the safety shield automatically extends overthe needle.

What is claimed is:
 1. A device for automatic injection of a productinto an injection site, the product being carried by a syringe having aneedle with a tip, the device comprising: a housing having a radial stopand configured to receive at least partially said syringe, said syringebeing movable with respect to said housing between an initial positionand an insertion position, distally spaced relative to said initialposition and in which the tip of the needle extends beyond a distal endof said housing; a safety shield coupled to said housing and movablewith respect thereto between a rest position, an activation position,proximally spaced relative to said rest position, and a safety position,distally spaced with respect to said rest position; a biasing elementfor causing the movement of said safety shield to said safety position;a trigger for causing the syringe to move from the initial position tothe insertion position; and an isolator element for isolating saidsafety shield from said biasing element when said safety shield is movedto the activation position, wherein said isolator element includes afirst ring having a flexible tooth provided with a distal abutmentsurface, said first ring being coupled to said biasing element in aproximal direction and coupled to said housing in a distal direction,said first ring being independent from said safety shield at leastbefore said safety shield is moved to said activation position, whereinsaid distal abutment surface rests on said radial stop before saidsyringe is in said insertion position.
 2. The device according to claim1, wherein said biasing element is a helical spring and a distal end ofsaid helical spring bears on a part of said first ring.
 3. The deviceaccording to claim 1, wherein said device further comprises a secondring fixed to said syringe.
 4. The device according to claim 3, whereinsaid flexible tooth comprises a sloping surface and said second ringcomprises a distal sloping surface, said distal sloping surface comes toabutment against said sloping surface so as to deflect said flexibletooth and disengage said flexible tooth from said radial stop, therebyfreeing said first ring from said housing when said syringe is in saidinsertion position.
 5. The device according to claim 4, wherein saidbiasing element is a helical spring having a proximal end bearing on apart of said second ring and a distal end bearing on a part of saidfirst ring.
 6. The device according to claim 1, wherein said safetyshield comprises at least one radial rim, wherein said first ring abutsagainst said radial rim when said syringe is in said insertion position,thereby coupling said first ring to said safety shield in the distaldirection under the biasing force of the biasing element.
 7. The deviceaccording to claim 1, wherein said flexible tooth is disengaged from theradial stop of the housing with said syringe in said insertion position.8. The device according to claim 1, wherein said trigger is releasableby movement of said safety shield to said activation position.
 9. Thedevice according to claim 1, wherein said trigger is in the form of apush button engaged to the housing by a projection on said push buttonsuch that the push button is allowed to move distally with respect tothe housing upon exertion of a distal pressure on a portion of the pushbutton by a user.
 10. The device according to claim 9, wherein saidfirst ring is released by a distal movement of said push button, therebyallowing said shield to be free to move to said safety position.